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## Class 8 (Old)

### Course: Class 8 (Old)>Unit 8

Lesson 6: Polynomials word problems

# Polynomial word problem: area of a window

Sal writes a polynomial expression that represents the total area of a window made of wood and glass. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• This is the foil method right?
• Yes you could use the FOIL method if you want to. The FOIL method is just a way to help you remember how to successfully solve binomials. It would come out with the same answer (that is if you did it correctly). It depends on weather you like the method or not (and if it makes sense to you).
• At , why is it 6x squared? Why do you make it squared.
• He made it squared since the 2 terms were 3X x 2X, so at this point you can add the two, like:
3 x 2 x X^1 x X^1, which is equal to 6X^2. Therefore, at that point he got 6X^2.

Hope the answer helped you out.
• What is -6z (z+3) I don't get it
• Andrea,
Remember the distributive property.
3*(2+4) =
3*2 + 3*4
You want to use the same distributive property.
-6z (z+3) =
(-6z)z + (-6z)*3 = Now multiply out the first part
-6
z*z + (-6z)*3 = and z*z is z² so
-6z² + (-6z)*3 = Now work on the second part
-6z² + -6*3*z = and 6*3 = 18 so
-6z² + -18z = and change the + - to a - so
-6z² - 18z

I hope that helps make it click for you.

P.S. If you do not remember the distributive property, try watching this video.
• hold on a minute, how were you able to distribute from parentheses to parentheses, isn't that not allowed in order of operations?
• (x+2)(x-1)=x(x-1)+2(x-1)=x*x-x*1+2*x-2*1, "foiling" follows directly from the order of operations.
• What if its a negative instead of a + i put a - right?
• yes, because a positive number plus a negative number is the same as subtracting a positive number
• I have a question that is similar to this video but I get stuck it's(5u-8)(4u-4) I see how you solved that one but on this one I can't figure out the right answer
• You can solve this if you use FOIL. First, you have to multiply- 8 * -4, which equals 32,
Then, multiply the outer terms. 5u * -4 = -20u
After, multiply the inner terms. 4u * -8 = -32u
Lastly, multiply 4u * 8u, which equals 32u^2
After you are done, combine the like terms.
Hope this helps.
• need help setting up this problem. The length of a rectangle is 9 inches more than its width ,Its area is 112 square inches
• I know that this isn't necessarily related to the video but, what is the FOIL method and if it is an acronym, what is it?
• The FOIL method is a way to multiply together two binomials. (Binomials are polynomials with two terms, like (x + 1) or (x^4 - 2x).) It stands for First, Outer, Inner, Last. This is an order you can use to multiply the terms inside the binomials.

For example, if I were to multiply (x + 1) and (3x + 2) together, it would look like this:
(x + 1)(3x + 2) = (x*3x) + (x*2) + (1*3x) + (1*2)
(x*3x) + (x*2) + (1*3x) + (1*2) = 3x^2 + 2x + 3x + 2
3x^2 + 2x + 3x + 2 = 3x^2 + 5x + 2
The first two terms, then the outer two terms, then the inner two terms, then the last two terms of each binomial are multiplied, then added together separately. Remember to simplify afterwards by adding together like terms.

Hope this helps!
• What do you mean by foil method; how are they different from other methods?
• Ann,
The FOIL method is just an easy way to remember what you are doing to multiply factors. For instance if you have (x+2)(3x+7) you would
FIRST - multiply the first terms (x*3x) = 3x²
OUTSIDE - Multiply the two outside terms (x*7) = 7x
INSIDE - Multiply the inside terms (2*3x) = 6x
LAST - Multiply the last terms (2*7) = 14